The objectives of this research are to study the synergistic effects that various combinations of ototraumatic agents have on hearing sensitivity and the cochlear sensory epithelium. Primary efforts have been directed at systematically studying the effects of combined impulse and continuous noise exposures. Scope of this study has expanded to include whole body vibration and drugs as other potentiating factors in impulse noise induced hearing loss. Chinchilla are used as the experimental animal. Noise-induced temporary and permanent threshold shifts are measured at regular intervals after exposure using the auditory evoked response measure. More complex auditory discrimination tasks such as intensity or frequency limens, or temporal integration functions, are obtained using conditioning techniques. At 30 days postexposure, the chinchilla are sacrificed, their cochleas infused with Araldite and flat preparation evaluations are made using phase contrast microscopy and thin sectioning techniques. At interesting locations, the tissue is analyzed with the electron microscope and, in some cases, with cytochemical procedures. The final evaluation of the particular noise exposure depends on a correlation of the noise parameters with the audiological and histological changes. These data are a necessary prerequisite for the establishment of a comprehensive Damage Risk Criteria for complex noise exposures.